[8u60] Request for approval/review: 8077249: Clean up around VM_GC_Operations

[Marcus Larsson]

Hi,

Please review and approve the following backport: JDK-8077249: Clean up 
around VM_GC_Operations.
The backport applied with some fuzzing and a simple manual merge of 
changes in collectorPolicy.cpp.

Issue:
https://bugs.openjdk.java.net/browse/JDK-8077249

JDK9 fix:
http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/e993a176f3d7

Backport webrev:
http://cr.openjdk.java.net/~mlarsson/8077249/webrev.00/

Thanks,
Marcus